Systems and methods of performing medical procedures

ABSTRACT

A medical method is provided, including a medical device having a distal assembly including at least one electrode and at least one treatment element, the medical device generating information regarding at least one of a physiological measurement and an operational parameter of the medical device; a plurality of surface electrodes affixable to a skin of the patient, wherein the surface electrodes are in electrical communication with the distal assembly to obtain position information of the medical device; and a processor pairing the position information and the at least one of a physiological measurement and an operational parameter of the medical device.

CROSS-REFERENCE TO RELATED APPLICATION

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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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FIELD OF THE INVENTION

The present invention relates to a method and system for pairingmulti-dimensional position information with device-measured treatmentinformation during a medical procedure.

BACKGROUND OF THE INVENTION

Medical procedures used to treat a variety of cardiovascular maladies,such as a trial fibrillation, typically involve the use of cathetershaving multiple sensors, electrodes, cryogenic chambers, or othermeasurement and treatment components to treat the diseased area of theheart or vasculature. Typically, such minimally invasive andintravascular devices are routed through a femoral artery or otherpassageway into the heart under guided fluoroscopy or other imagingtechniques. For example, monoplane or biplane fluoroscopic imaging canbe used estimate the position of the catheter within the heart. Anothermethod to determine position information for an inserted medical deviceduring cardiac procedures is to measure the opposition to time-varyingelectric current in an electric circuit, or impedance, provided by thetissue surrounding the target tissue. This is typically achieved byplacing one or more impedance sensors or electrodes on or in thepatient's body and measuring the impedance or electric potential betweenone of the sensors or electrodes and an electrode or sensor on thecatheter.

In addition to the use of imaging to monitor or guide the position of amedical device within a patient, there are often numerous otherinformational parameters provided, monitored, and/or recorded both withrespect to both the patient and the actual medical device. For example,during a therapeutic application such as cardiac or other tissueablation, measurements may be taken by the medical device as to tissuetemperature, electrical activity of the tissue, various impedancemeasurements of the tissue and/or surrounding environment. In addition,parameters such as pressure, structural integrity (e.g. leak presence),diameter of a device (where balloons may be included, for example),fluid flow rate, etc. may be taken with respect to the device itself.Such device-originated information may be provided on a control panel,status monitor or other display unit or device within thetreatment/operating room.

Given the often numerous, independent sources of information regarding aparticular procedure presented to a physician during treatment, it mayprove difficult to keep track of the various parameters regarding devicepositioning, operation, and the efficacy of the delivered treatment. Inview of the above, it is desirable to provide systems and methods of usethereof for pairing positional information of a medical device within apatient with device-based operational or physiological information foruse during a medical procedure.

SUMMARY OF THE INVENTION

The present invention advantageously provides medical methods andsystems for performing a medical procedure. In particular, a medicalsystem is provided including a medical device having a distal assemblyincluding at least one electrode and at least one treatment element, themedical device generating information regarding at least one of aphysiological measurement and an operational parameter of the medicaldevice; a plurality of surface electrodes affixable to a skin of thepatient, where the surface electrodes are in electrical communicationwith the distal assembly to obtain position information of the medicaldevice; a processor pairing the position information and the at leastone of a physiological measurement and an operational parameter of themedical device. A reference electrode may be affixable to the skin ofpatient, the reference electrode being in electrical communication withthe distal assembly, and the treatment element may include aradiofrequency ablation element or a cryogenic ablation element. Theplurality of electrodes may include at least three pairs of surfaceelectrodes that cooperate with the distal assembly to measure electricpotential in three different planes. The physiological measurement mayinclude a measured tissue impedance, and the position information andthe at least one of a physiological measurement and an operationalparameter of the medical device may be obtained sequentially orsimultaneously.

A medical method is also provided, including inserting a medical deviceinto the body of a patient; obtaining position information of themedical device; treating a tissue site with the medical device;obtaining at least one of a physiological measurement of the tissue siteand an operational parameter of the medical device; pairing the positioninformation with the at least one of a physiological measurement of thetissue site and an operational parameter of the medical device; andmodifying the treatment of the tissue site based at least in part on thepaired information. Modifying the treatment may include terminating thetreatment. The method may include graphically displaying the pairedinformation.

Another medical method is provided, including applying at least threepairs of surface electrodes to the skin of a patient; applying anelectric potential between each of the at least three electrode pairs;providing a medical device having a distal assembly with at least oneelectrode and at least one ablation element; inserting the medicaldevice into the body of the patient; obtaining three-dimensionalposition information of the medical device; ablating tissue at a tissuesite with the ablation element; measuring an impedance proximate thetissue treatment site; pairing the position information with themeasured impedance; processing the paired position information and themeasured impedance into a computer readable signal; graphicallydisplaying the paired information; and modifying the operation of theablation element based at least in part on the paired information.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 a is a front view of an embodiment of a medical systemconstructed in accordance with the principles of the present invention.

FIG. 1 b is back view of a part of the medical system in FIG. 1 a;

FIG. 2 is another schematic of a medical system constructed inaccordance with the principles of the present invention;

FIG. 3 is a graph showing the sequence and duration of applyingelectrical current across various electrodes of the medical systems ofFIGS. 1 a-2;

FIG. 4 is a flow chart of a medical method of use of the medical systemsof FIGS. 1 a-2 in accordance with the principles of the presentinvention;

FIG. 5 is a side view of an exemplary medical device used in conjunctionwith the method shown in FIG. 4;

FIG. 6 is a front view of another exemplary medical device used inconjunction with the method shown in FIG. 4;

FIG. 7 is a perspective view of yet another exemplary medical deviceused in conjunction with the method shown in FIG. 4;

FIG. 8 is a side view of an exemplary medical device used in conjunctionwith the method shown in FIG. 4;

FIG. 8 a shows the distal end of the medical device shown in FIG. 8; and

FIG. 9 shows the medical device shown in FIG. 7 proximate a tissueregion to be treated in the heart.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides systems and methods of use thereof forpairing positional information of a medical device within a patient withdevice-based operational or physiological information for use during amedical procedure. In particular, device-originating measurements andinformation can be paired with device positioning information to providea graphical or visual output that includes both device position relativeto the anatomy and physiology of the patient, as well as locationspecific measurements and properties overlayed or otherwise included forthe physician's reference during a medical procedure. Referring now tothe drawings in which like reference designators refer to like elements,there is shown in FIGS. 1 a and 1 b, front and back views of anexemplary medical system pairing positional information withdevice-based operational or physiological information and designatedgenerally as “10.”

The system 10 generally includes a medical device 12, such as acryogenic or radio-frequency (“RF”) ablation catheter and the like. Themedical device 12 generally includes an elongate body with a treatmentportion having one or more energy transfer elements at a distal endportion. The medical device 12 may be adapted for percutaneous orsurgical insertion into the body, and in particular, into thecardiothoracic region of a patient. The system 10 further includes oneor more surface electrodes 14 positionable about the exterior of thepatient (such as on the skin, for example) that include impedancemeasurement capabilities or other features allowing the detection,receipt, and/or transmission of an electrical signal. Each surfaceelectrode 14 may have an adhesive surface that is removably affixable tothe skin, or each surface electrode 14 may be implanted under the skin.Optionally, conductive gel (not shown) may be applied to the skinsubjacent to the surface electrode 14 to increase the conductivity oradhesiveness between surface electrodes 14 and the body of the patient.

In an exemplary embodiment, three pairs of surface electrodes 14 areadhered to the skin to provide three-dimensional position information inx, y, and z planes. For example, as shown in FIGS. 1 a and 1 b, surfaceelectrodes 14 include surface electrodes 16 and 16′ adhered to the rightand left sides of the chest of the patient; surface electrodes 18 and18′ adhered to portions of the neck and thigh respectively; and surfaceelectrodes 20 and 20′ adhered to the chest and back respectively.

Additional surface electrodes 14 may be adhered to the skin of thepatient as desired in any number of desired locations to provideadditional positional information, precision, and/or accuracy, asdescribed more below. The surface electrodes 14 may be connected to apower supply, such as a generator, a display 32 (FIG. 2) and/or othersignal processing components (such as those disclosed in U.S. Pat. Nos.5,697,377 and 5,983,126, the entirety of each of which is incorporatedherein by reference) to process and display information regarding orrelating to the electrical signals sensed by the surface electrodes 14.

Continuing to refer to FIG. 1 b, in addition to surface electrodes 14,one or more reference electrodes 22 may be adhered to the skin of thepatient in a similar fashion to that of the surface electrodes 14, oralternatively be disposed within the body of the patient, for example,at a location proximate or within the heart. For example, as shown inFIG. 1 b reference electrodes 22 and 22′ may be adhered to the back ofthe patient on opposite sides of surface electrode 20′. Referenceelectrodes 22 and 22′ may be grounded such that they are operable toreceive RF energy during an RF energy treatment provide by the medicaldevice 12. Alternatively, reference electrodes 22 and 22′ may include agrounded, non-adhesive plate positionable beneath the patient.Additionally, any or all of the surface electrodes 14 may be selectivelyoperable as ground electrodes during, for example, delivery of RF energyin a unipolar mode, as discussed in more detail below.

The medical device 12 of the system 10 may include one or more ablationelements 24 coupled to a distal assembly 26 of the medical device 12.The distal assembly 26 of the medical device 12 is the treatment portionof the medical device 12 navigated towards and placed proximate to thetarget tissue to be treated. For example, exemplary medical devices 12having ablation elements 24 are shown in FIGS. 5-8 a and are discussedin more detail below. The ablation elements 24 may include, for example,RF electrodes, cryogenic chambers, ultrasound emitters, laser emittingdiodes, and other ablative elements known in the art.

The medical device 12 may be used in conjunction with the surfaceelectrodes to provide positioning information of the device within thepatient. In particular, in addition to the ablation elements 24, each ofthese exemplary medical devices 12 shown in FIGS. 5-8 a may include oneor more electrodes 28 coupled to the distal assembly 26 operable totransmit electrical energy and/or measure impedance activity between apair of the surface electrodes 14. Based on this electrical or impedanceactivity, the position of the medical device 12 may be tracked andmonitored as it is advanced towards the target tissue and as itnavigates from one treatment site to the next. For example, electricalpotential localization (EPL) may used to localize or triangulate theposition of the electrodes 28 in three-dimensional space, allowing thesurgeon to accurately determine the position of the medical device 12with respect to surrounding tissues.

Localization and triangulation of the electrodes 28 may be obtained bymeasuring and recording the electric potential or impedance activitybetween two or more of the surface electrodes 14 and between one or moreof the surface electrodes 14 and the electrodes 28, in sequence orsimultaneously. For example, an electric potential, which may beorthogonal, may be applied across surface electrodes 16, 16′, 18, 18′,20, and 20′ in sequence or simultaneously and sensed and measured byelectrodes 28. From this measurement of electric potential or impedance,the position of the medical device 12 in x, y, and z planes may beextrapolated based on the known or calculated interelectrode distancesbetween the surface electrodes 14. Any of the electrodes 28 may befurther selectively operable to extrapolate the position of a portion ofthe medical device 12 for increased accuracy. For example, theembodiments of exemplary medical devices 12 shown in FIGS. 5-8 a eachmay have one or more of electrodes 28 included on their respectivedistal assemblies 26. Should the surgeon desire to determine theposition of a particular portion of the medical device 12, a particularelectrode 28 may be activated to determine that position.

The frequency of the electric fields generated and applied to thesurface electrodes 14 may be different between two surface electrode 14pairs to minimize interference and to isolate each potential orimpedance measurement. For example, the current may be applied betweensurface electrodes 16 and 16′ at a frequency of 30 kHz and betweensurface electrodes 18 and 18′ at a frequency of 40 kHz. The duration atwhich each electric field is applied may be constant or variabledepending on the desired measurement. For example, if the “x” positionof the medical device 12 is the desired measurement during a treatment,the voltage potential applied to surface electrodes 14 that measurepotential or impedance along the “x” position of the medical device maybe applied for a longer duration of time than the electrodes thatmeasure potential or impedance in the “y” or “z” positions.

In addition to localization information, the system 10 includesphysiological assessment information or device operating parametersprovided by the medical device 12. In particular, the ablation elements24 and/or electrodes 28 may be operable to obtain physiologicalassessment information, such as impedance and temperature measurements,tissue contact assessment information, fluid flow rates, pressures,electrical activity, etc. The distal assembly 26 may have a plurality ofelectrodes 28 or other sensors facilitating the monitoring, measuring,and or recordation of these exemplary parameters.

Referring now to FIG. 2, the system 10 may further includes a processor30 to process positional information and the physiologicalassessment/device operational information. For example, locationinformation obtained from the surface electrodes 14 and physiologicalassessment information obtained from the medical device 12 may each berelayed through one or more wires to the processor 30. The processoroperates to multiplex or pair the measured position and physiologicalassessment information into one or more computer readable signals. Thecomputer readable signal may then be displayed on a display 32 where avisual image of the combined position and physiological data may beshown. The processor 30 and the display 32 may further be incommunication with a database 34 that stores patient statistics,treatment history, or historic position and physiological assessmentinformation. For example, real-time position and physiologicalinformation may be paired with or displayed with historic information onthe display 32 as an easy-to-read single source of treatment informationbefore, during, or after a medical procedure at a specific locationwithin the patient's anatomy. As such, as the surgeon moves the medicaldevice 12 to a different location, he can monitor both the physiologicalassessment information and position information on a single display forthat specific location.

The position and physiological assessment information may be pairedsequentially or simultaneously. For example, a process of obtainingreal-time position and device-originated information is shown in FIG. 3.Voltage potentials “Vx,” Vy”, and “Vz” and impedance measurements “Zu”and Zb” are each processed and recorded in sequence and for the sametime duration. Vx represents the measurement of the voltage potentialapplied between surface electrodes 16 and 16′ when a current is applied;Vy represents the voltage potential applied between surface electrodes18 and 18′ when a current is applied; Vz represents the voltagepotential applied between surface electrodes 20 and 20′ when a currentis applied; Zu represents the impedance measured between electrode 28 orablation elements 24 and either reference electrodes 22 or 22′ when themedical device 12 is operable to deliver unipolar RF energy; and Zbrepresents the impedance measured between two or more electrodes 28 orablation elements 24 disposed on the medical device 12, for example,during bipolar transmission of RF energy. Some or all of thesemeasurements may be recorded in any sequence and for any time duration.For example, if a measurement of the x, y position of the medical device12 is desired, Vx and Vy may be recorded and multiplexed with or withouta Zu and/or Zb measurement.

Alternatively, any or all of Vx, Vy, Vz, Zu, and Zb may be impedance orelectric potential measurements, and may be measured from constant,intermittent, or phased current and may be obtained simultaneously. Forexample, when providing both unipolar and bipolar RF energy to thetreatment site, physiological assessment information, such as impedancemeasurements Zu and Zb, temperature, or contact assessment, can be madeover a pre-determined period of time. For example, Vx, Vy, and Vz can becontinuously measured as medical device 12 is advanced and is navigatedtowards the target tissue. Upon reaching the target tissue site, bipolarand/or unipolar RF energy may be transmitted to the target tissue, incombination or in sequence. As treatment energy is transmitted to thetarget tissue, the measured impedance may change. Any changes can bemeasured by Zu (unipolar) and Zb (biopolar) and may be multiplexed orpaired by, for example, the processor 30 (FIG. 2), with Vx, Vy, and Vzinformation into one or more computer readable signals that provide bothposition and physiological assessment information. The processedposition and physiological assessment information can then be visuallydisplayed on display 32 during a procedure to provide overall treatmentassessment information. Optionally, the medical device 12 may includeadditional electrodes or sensors that may act in combination or may bemultiplexed with Vx, Vy, Vz, Zu, and/or Zb to yield more than positionor impedance information. For example, the unipolar or bipolar RFablation elements 24 may be operable to both sense impedance and ablatetissue. Additionally, temperature information obtained fromthermocouples coupled to medical device 12 can be multiplexed with thepositional, potential, or impedance information obtained from Vx, Vy,Vz, Zu, and/or Zb to provide information about the efficacy of thetreatment.

The system 10 can further be adjusted and calibrated to compensate forvariations in measurements owing to, for example, respiration ormovement of the patient. For example, because the patient is breathingduring treatment, Vx, Vy, Vz, Zu, and Zb measurements may vary duringrespirations. The measured impedance may decrease upon exhalation andincrease upon inhalation. These variations can be measured and off-setby calibrating the multiplexed signal during an initial assessmentperiod before treatment. Alternatively, a filter can be applied to anyof the measured Vx, Vy, Vz, Zu, and Zb signals to eliminate noise andcollateral effects on the measured potential or impedance.

Referring now to FIG. 4, an exemplary method of treatment using thesystem 10 discussed above is shown. Initially, the surface electrodes 14and reference electrodes 22 are applied to the skin either while thepatient is in a supine position or while standing up, and an electricpotential is applied to the surface electrodes 14 (Step 210). Next, amedical device 12, for example, those disclosed in FIGS. 5-8 a, isadvanced through the vasculature towards the target tissue(percutaneously or surgically, for example) (Step 211). For example, asshown in FIG. 9, in performing a procedure to correct atrialfibrillation, the medical device 12 may be inserted into the venoussystem and navigated into the patient's heart, through the inter-atrialseptum, and the into the left atrium of the patient where the targettissue resides. As the medical device 12 is navigated through thevasculature, voltage potential and/or impedance measurements aremeasured and recorded, as discussed above, by one or more pairs ofsurface electrodes 14 and electrodes 28 and its position may be visuallydisplayed for the operator or physician. When the medical device 12reaches it its target site, a medical procedure, such as RF ablation,cryoablation, or the like may be initiated. During this procedure,various operating parameters such as temperature, tissue contactassessment, tissue impedance measurements, flow rates of fluids throughthe device, pressure in or around the catheter, etc. may be monitored orprovided by the medical device by one or more sensors. The positionalmeasurement data is then multiplexed, paired, or otherwise combined withthe operational, device-based information, and may include, for example,the impedance data measured and recorded between one or more electrodes28 or ablation elements 14 (bipolar) and between one or more electrodes28 and reference electrodes 22 and/or 22′ (unipolar) (Step 212). Thispaired data may then be processed by processor 30 and displayed toidentify the operational parameters (such as temperature, tissueassessment, etc.) at specific locations (as provided by the surfaceelectrodes) for the medical device. This information may be used todetermine or otherwise asses the efficacy of the treatment or the statusof the medical device.

Based on the data retrieved and assessed in Step 212 and displayed ondisplay 32, the medical procedure may then be continued at a differenttreatment site or adjusted (Step 213). For example, energy delivery maybe initiated, continued, or terminated based on the operationalinformation provided by the device in conjunction with the position ofthe device. For example, a target tissue impedance level of an ablationsite can be predetermined before treatment and treatment may be stoppedshould that target tissue impedance level be reached. In particular, ifthe target tissue is frozen or burned, the associated changes in theelectrophysiology of the target tissue can be detected by the impedancemeasurements proximate the treated tissue. Further, by pairing thisinformation with the positional information, the physician can visuallyidentify where these impedance levels are being recorded and adjust thetreatment delivery and/or positioning based on such information.

In embodiments of the present invention where the medical devices 12 isan RF ablation catheter, Zu and/or Zb, may be measured proximate thepulmonary vein (“PV”) antrum or the Fossa-Ovalis. For example, RF energymay be delivered to the PV antrum, but care in positioning the medicaldevice 12 is typically advised to avoid causing a pulmonary veinstenosis. Impedance measurements Zu and/or Zb may be measured incombination with Vx, Vy, and Vz and the paired data may be correlated todetermine the accuracy of RF delivery at the PV antrum. For example, ahigher impedance indicates that the distal assembly 26 of the medicaldevice 12 may be positioned within the pulmonary vein and a lowerimpedance indicates the medical device 12 may be positioned in theatrium. Alternatively, should the target tissue be the Fossa-Ovalis, oneor more electrodes 28 may be positioned proximate a septal penetratorcoupled to the distal assembly 26 of the medical device 12, and Zuand/or Zb in combination with Vx, Vy, and Vz, may be measured todetermine when contact is made with the Fossa-Ovalis. For example, animpedance measurement indicative of a lack of muscle contractions mayfurther indicate that the Fossa-Ovalis has been contacted.

The completeness or efficacy of any or all of the above procedures, orany other procedure using the above method, may be based in part orfully on any or all of Vx, Vy, Vz, Zu, and Zb measurements (Step 214) orhistoric information recorded and measured previously from the patient,or a combination of each. For example, in an embodiment where acryogenic procedure is performed, if Zu and/or Zb reach a predeterminevalue, or if the time rate of change of Zu and/or Zb reaches zero, thetarget tissue may be frozen and the treatment may be terminated.Alternatively, if the treatment is not complete, Steps 212 and 213 maybe repeated and/or modified based on real-time or historic informationuntil the desired measurements are reached. For example, if measurementsof Vx, Vy, and Vz, determine that the medical device 12 is not in thecorrect position for treatment, Steps 212 and 213 can be repeated untila either the desired target area is treated or a desired tissuecondition is achieved.

Based on the measured data obtained from Vx, Vy, Vz, Zu, Zb, and/orother sensor measurements from medical device 12, it is contemplatedthat various tissue or treatment assessment information may be measured,calculated, or correlated from the processed paired data. For example,lesion quality data, tissue contact data, tissue anatomy data,respiration data, electrogram amplitude and fractionation data, localactivation timing data, fibrillatory wave (F-wave) cycle length data,dominant F-wave frequency data, action potential duration data (APD),refractoriness data, and/or combinations of the above may all becalculated. Any of the above data may be measured during Step 212 todetermine if treatment needs to be modified in Step 213. For example,the delivery ratio of unipolar to bipolar energy may be modified basedon any of the above calculated data.

In another example, measurement of APD data may be paired or multiplexedwith data measured from a monophasic action potential (MAP) sensorcoupled to the medical device 12 and positioned proximate the treatmentsite. For example, MAP and APD may be recorded sequentially orsimultaneously with any of the above data, wherein the MAP sensor mayrecord action potential signals from the surrounding tissue in the rangeof, for example, 0.05 Hz to 500 Hz, and increase the calculation timefor APD data acquisition. From this data, a dispersion assessment ofaction potential durations may be calculated. The MAP and APD data mayfurther be correlated with Vx, Vy, Vz, Zu, Zb, and/or any of the abovedata to provide endocardial surface information which may be visualizedby the surgeon during a treatment. Based on MAP, APD, and othercalculated data discussed above, thresholds may be established above orbelow which energy is delivered to a treatment site.

Optionally, patient imaging, such as MRI, CT, X-ray, ultrasound, and thelike, may be performed before and/or after the above method is completedto provide anatomical data of the patient to assess the efficacy of thetreatment. For example, in an RF ablation treatment, imaging of thetarget issue may be performed before and after treatment to determinethe extent of the ablation. If the desired result is not achieved, Steps211-214 may be repeated.

Referring now to FIG. 5, an exemplary medical device 12 is shown thatmay be used with the above system 10 and method. The medical device 12is an RF ablation catheter having a distal assembly 26 includingablation elements 24 in communication with a generator and one or moreelectrodes 28. In the illustrated embodiment, the distal assembly 26 ofthe medical device 12 includes a carrier assembly having three carrierarms including ablation elements 24 as described in U.S. Pat. No.7,468,062, the entirety of which is incorporated herein by reference.The ablation elements 24 and/or electrodes 28 may be operated withsurface electrodes 14 (not shown) to measure Vx, Vy, Vz, Zu, Zb and/orany of measurements discussed above, and deliver unipolar and bipolar RFenergy to tissue, in particular the septal wall, in accordance with themethod described above. Optionally, one or more MAP sensors or anelectromagnetic localization element (ELE) may be included on medicaldevice 12 and may provide measurements in accordance with the methoddescribed above.

Referring now to FIG. 6, another exemplary medical device 12 is shownthat may be used with the above system 10 and method. The medical device12 is an RF ablation catheter having a distal assembly 26 includingelements 24 in communication with a generator and one or more electrodes28. In the illustrated embodiment, the distal assembly 26 of the medicaldevice 12 includes a carrier assembly having four carrier arms includingablation elements 24 as described in U.S. Pat. No. 7,429,261 theentirety of which is incorporated herein by reference. The ablationelements 24 and/or electrodes 28 may be operated with surface electrodes14 (not shown) to measure Vx, Vy, Vz, Zu, Zb and/or any of themeasurements discussed above, and deliver unipolar and bipolar RF energyto tissue, in particular the atrial wall, in accordance with the methoddescribed above. Optionally, one or more MAP sensors or an ELE may beincluded on medical device 12 and may be measured in accordance with themethod described above.

Referring now to FIG. 7, yet another exemplary medical device 12 isshown that may be used with the above system 10 and method. The medicaldevice 12 is an RF ablation catheter having a distal assembly 26including ablation elements 24 in communication with a generator and oneor more electrodes 28. In the illustrated embodiment, the distalassembly 26 of the medical device 12 includes a flexible and deflectablehelical wire having ablation elements 24 as described in U.S.application Ser. No. 11/471,467 the entirety of which is incorporatedherein by reference. The ablation elements 24 and/or electrodes 28 maybe operated with surface electrodes 14 (not shown) to measure Vx, Vy,Vz, Zu, Zb and/or any of the measurements discussed above, and deliverunipolar and bipolar RF energy to tissue, in particular the pulmonaryvein, in accordance with the method described above. Optionally, one ormore MAP sensors or an ELE may be included on medical device 12 and maybe measured in accordance with the method described above.

Referring now to FIGS. 8 and 8 a, yet another exemplary medical device12 is shown that may be used with the above system 10 and method.Medical device 12 is a cryogenic catheter including an elongate bodydefining a proximal and distal end and one or more fluid pathways therethrough. The cryogenic catheter may include at least one expandablemember 36 defining a cryogenic chamber 38 coupled to the distal assembly26 of the device. The expandable member 36 is further in fluidcommunication with a cryogenic fluid source. One or more electrodes 28may be coupled to the catheter at the distal assembly 26. For example,as shown in FIG. 7 a, the expandable element may be disposed between twoor more electrodes 28 or may include one or more electrodes 28 coupledto the expandable member's 36 surface. Any of the electrodes 28 maycooperate to measure Zu, Zb, and/or Vx, Vy, or Vz. Optionally, one ormore leak detectors or pressure sensors may be positioned about thedistal assembly 26 of the catheter and the measured information fromthese components may be paired or multiplexed with any of the abovemeasurements.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

What is claimed is:
 1. A medical system comprising: a medical devicehaving a distal assembly including at least one electrode and at leastone treatment element, the medical device obtaining informationregarding impedance; a plurality of surface electrodes affixable to askin of a patient, wherein the surface electrodes are in electricalcommunication with the distal assembly to obtain position information ofthe medical device; an energy generator in electrical communication withthe distal assembly and the plurality of surface electrodes, thegenerator being configured to deliver ablation energy to the treatmentelement in unipolar mode and bipolar mode simultaneously; a processor,the processor being configured to obtain the information regardingimpedance from the medical device and the position information of themedical device from the plurality of surface electrodes simultaneouslywhen ablation energy is being delivered to the treatment element, theprocessor pairing the position information and the information regardingimpedance.
 2. The medical system of claim 1, further comprising areference electrode affixable to the skin of the patient in electricalcommunication with the distal assembly.
 3. The medical system of claim2, wherein the treatment element is a radiofrequency ablation element.4. The medical system of claim 1, wherein the plurality of electrodesincludes at least three pairs of surface electrodes.
 5. The medicalsystem of claim 4, wherein the at least three pairs of surfaceelectrodes cooperate with the distal assembly to measure electricpotential in three different planes.